The present invention relates generally to pressure cylinders (i.e. working cylinders) having dampening means for cushioning movement of a pressure operated piston at its opposite ends of travel. More particularly, the invention pertains to a pressurized medium activated working cylinder with a piston supported so that it can move longitudinally in a cylinder chamber between two end positions, with two end parts that close the cylinder chamber at the ends and that have devices for feeding and discharging pressurized medium, with a piston rod that is connected to the piston and that penetrates through at least one of the end parts in a sealed configuration, and with a device for damping the movement of the piston when it approaches each end position, wherein this device has a damping pin and a receptacle opening that matches this pin on the side facing each end part, and this opening is connected to the corresponding device for feeding and discharging pressurized medium and the damping pin is inserted into this opening when the piston approaches the end position.
A known working cylinder with dampening means is shown in EP 0 735 280, which includes a damping sleeve that is coaxial to the piston rod on each of the two opposite end faces of the piston. Each damping sleeve matches a coaxial receptacle opening in the adjacent end part. This opening is connected to a type of pocket opening that is completely integrated in the end part and that is connected to a pressurized medium feeding and discharging channel in the end part. The braking of the piston at the end of the stroke, i.e., when the piston approaches the end position, happens in such a way that the passage cross section for the pressurized medium flowing out of the decreasing section of the cylinder chamber is substantially reduced by the insertion of the damping sleeve into the receptacle opening. Because the damping sleeves must have an exact axial length, and the extending piston must be held completely in the matching end part for the corresponding end positions, so that the piston essentially contacts the end part, the installation size of the working cylinder must be lengthened for the damping sleeves. This applies even more so for the known working cylinder, since in each end part there is an additional check valve with a valve body that extends into the cylinder chamber, and thus for the out-stroke of the piston from its end position, it enables rapid filling of pressurized medium into the now increasing cylinder chamber section. For certain applications which require a relatively short working cylinder the type of known working cylinder cannot be used.
Other solutions for working cylinders with end position damping of the piston are described in EP 1 041 293 A2 and U.S. Pat. No. 3,136,225. A valve element supported with a helical spring is provided for the piston of these working cylinders, such that the outward flow of the pressurized medium from the decreasing cylinder chamber section is throttled before reaching the end of the stroke. However, due to reasons of stability, these working cylinder constructions require relatively thick piston rods, aside from the fact that they are relatively complex and expensive.
It is an object of the present invention to provide a pressurized fluid operated cylinder, i.e. working cylinder, with end positioning dampening of the piston which has a short length construction that is simple in design and which lends itself to reliable operation.
A working cylinder according to the invention has a damping device which includes a damping pin and a receptacle opening that matches the pin arranged eccentric to the side near the piston rod, wherein the receptacle opening opens into a part projecting from each end part or from the piston into the cylinder chamber. This part matches a corresponding recess on the opposing side of the piston. In order to ensure that the damping pins find the corresponding end position during the in-stroke of the piston for reliably entering into the receptacle opening, the piston has an associated guide device.
Due to the fact that the damping pin with its matching receptacle opening is located to the side of the piston rod, the arrangement of the damping pin and the recess surrounding the pin is independent of the attachment of the piston rod to the piston. The receptacle opening into the cylinder chamber for the damping pin permits a short length construction of the working cylinder, without adversely affecting end position damping of the piston.
In order to achieve rapid filling of the increasing section of the cylinder chamber and thus quick piston movement for the out-stroke of the piston from its end position, a check valve that is connected to the devices for feeding and discharging pressurized medium can be arranged in the corresponding end part with a flow direction oriented into the cylinder chamber such that the valve has no parts projecting into the cylinder chamber. The check valve preferably has a flat shape with a lip seal on the side facing the cylinder chamber.
Preferably, sealing means are arranged in the receptacle opening so that the damping pin can be sealed in at least one flow direction during insertion into the open receptacle, whereby effective end position damping can be achieved. The end parts may contain channel means that are connected to the devices for feeding and discharging pressurized medium, that open into the cylinder chamber, and that are associated with throttle means which affect the flow of pressurized medium, and which can be adjusted, if necessary. By virtue of such channel means, for the in-stroke of the piston into the corresponding end position after insertion of the damping pin into the matching receptacle opening, the pressurized medium acting as the piston can be throttled so that the piston can completely reach its end position.
A guiding device for the piston can be provided that has at least one rod extending the length of and parallel to the cylinder chamber, with the piston being sealed against this rod and, preferably, with the rod being fixed at the end parts. Alternatively, the guiding device of the piston can be effected by other means, such as by means of a non-circular cross section piston rod and/or piston and guide or guides in the corresponding end part in the tubular body or bodies surrounding the cylinder chamber.